Speedometer



Feb. 19, 1929.

F. F. DORSEY SPEEDOMETER Filed March 26, 1927 Patented Feb. 19, 1929. y K

Uirnn STATES PAT-ENT oFFlcE,l

FARNUM F, DORSEY, OF ROCHESTER, NEW YORK, ASSTGNOR TO NORTH. EAST ELECTRTC COMPANY, OF ROCHESTER, NEW YORK, A CORPORATION 0F NEW YORK.

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Application-filed March 26, 1927.

This invention relates to speedometer-s of the type in which a cup-like pivotally mounted indicator, with a depending skirt of electrically conductive material, is turned, against the opposition of a spring, by the inductive effect of a stationary magnet and ay rotary armature, the movement of the indicator being proportionate to the speed of rotation of the armature.

In a speedometer mounted upon the instrument-board of a motor vehicle it is usually desirable that the drive-shaft extend from the rear of the'instrument either in a horizontal position or in a position at a considerable angle with the vertical. It is also desirable that the pivot-bearings of the indicator be mounted on fixed supports on theframe of the instrument. To secure these advantages in instruments of the forms previously used, it has vbeen necessary to introduce various complications into the structure, such e as gears or flexible shafts, to connect the driveshaft with therotor, and overhanging arms to support the pivot-sta-ffbearings and the indicator.

The object of the present invention is to secure the advantages of a rear-driven instrument while avoiding the disadvantages 'just referred to, particularly the use of lgearing or sharply curved flexible shafts. To this end the indicator, magnet and rotary armature are so formed and related that they have certain approximating and overlapping portions sufficient for their functional cooperation, altho the pivotal axis of the indicator and the axis .of rotation of the armature are arranged at such an angle that the armature may be mounted directly upon a rearwardlyextending drive-shaft.

In the accompanying drawings, Fig. 1 is a sectional side elevation of a speedometer embodying the present invention, and Fig. 2 is a section on the line 2 2 in Fig. 1.

The invention is illustrated as embodied in an instrument having an indicator 3, drawn from some conductive sheet material such as aluminum, in the form of a truncatedy cone. This indicator is fixed to a pivot staff 4 which is upwardly and forwardly inclined at an angle of 45. The staff has bearings mounted in stationary frame members 5 and 6, and the usual hair spring 7 attached to the staff, tends to hold the indicator normally in zero position. The conical skirt of the indicator Serial No. 178,758.

has the usual graduations to indicate speed in miles or kilometers per hour, which are visible through an opening in the face plate or dial 8 of the instrument. This dial may be covered with glass 16 inthe usual manner.

The instrument has a cylindrical housing 18, of which the rear wall is shown as embodied in a casting 9 comprising part of the frame of the instrument. Upon this rear frame member is supported a permanent magnet 10 in the form of an open ring, the opening being at the top of the magnet so as to provide, at that point, two polar extremities 11. The armature 12 isv in the form of a disc of sheet steel or other suitable magnetic material, having at its periphery a series of rearwardly projecting lingers 14;. This armature is fixed to and actuated by ahorizontal drive shaft 13 which turns inbearings in the frame member 9.

The axis of the armature is so located that the upper part of the armature approaches close to the lower surfaces of the polar extremities 11. The indicator is so mounted that the rear part of its'conical skirt projects intothe space between the magnet and the armature. F or some distance near the polar extremities of they magnet, therefore, the parts have a cooperative relation such that flux passes downwardly from one pole of the magnet into one or more of the fingers 14 on the armature and through other ngers, to the other pole of the magnet. The flux so conducted passes twice through the skirt of the indicator. When the armature rotates these concentrated lines of force are caused to traverse the metal of the indicator in the direction of rotation of the armature, so as to produce an inductive drag upon the indicator in a well-known manner.

The relation of the parts described is such as to permit the indicator to have a suitable form for the displayy of numerals, while the armature may be mounted directly upon a horizontal drive shaft, thus dispensing with the use of gearing, or other undesirable ydriving connections. At the same time, the indicator may be of the simplest form, with its pivot staffv mounted in stationary bearings without the necessity of relatively delicate overhanging arms. lFurthermore, ample space is provided for an odometer 15, visible through the face plate of the instrument in the usual position. This odometer may conf veniently be driven by power derived from the drive shaft 13 through a worm wheel 17. The construction of the odometer and of its drive mechanismv is not inlly shown and described herein, since it constitutes no part of the invention claimed.

Although the magnet l0 is approximately circular in general form, so as to permit it to be of as great a length as possible, its polar extremities are preferably bent downwardly somewhat, as shown in Fig. 2, so as to secure a minimum air gap between the magnet and the indicator at this point.

it will be understood that where certain parts are .sho-wn and claimed as having the relation oi upper and lower, horizontal and vertical, etc., these terms are used as descriptive merely of the relative positions of the parts since the parts so associated will operate in any absolute position.

The invention claimed is:

l. In a speedometer, the combination of a spring-controlled, pivotally mounted indicator, With an electrically conductive conical skirt, a magnet, in the form o'l an open ring, with its ends overlapping and lying close to the outer' surface ot the rear part of said skirt, and a rotary armature, having time concentrating projections ot magnetic material, journalled in position to approilgmate the inner surface oi the rear part of the skirt the axis of rotation oi the armature forming a substantial angle with the pivotal axis of the indicator.

2. n a speedometer, the combination of a housing oi' a form generally cylindrical about a horizontal axis, a magnet, of substantially circular form, with a gap and two polar extremities at its upper part, the magnet being approximately coaxial with the housing and iiXed in the rear part et the housing, a rotary arn'iature, having flux-concentrating projections, of less diameter than the magnet and journalled on a horizontal axis so located that the uppermost part oi' the armature moves close to the polar extremities oi" the magnet, a pivot-staff, in front of the magnet and the armature, mounted to turn upon an axis upwardly and forwardly inclined, and an indicator, mounted on said pivot-stati), having a conical conductive skirt o'l which the rear part projects into the space between the adjacent parts ot the magnet and the armature.

Si. ln a speedometer, the combination oit a spring-controlled indicator, Withan electrically conductive conical skirt, pivotally mounted on an inclined axis, a magnet. with its polar extremities lying close to one surface ol said skirt at its rearmost part, and a rotary armature, having' flux-concentrating projections of magnetic material, journalled on an axis forming a substantial angle with that of the indicator and in position such that said projections revolve in a path approximating the surface ot said skirt opposite that to which the magnet-poles are adjacent.

FARNUM F. DORSEY. 

